Data delivery in conjunction with a hybrid automatic retransmission mechanism in CDMA communication systems

ABSTRACT

Techniques for delivering data recovered by a HARQ entity in proper order to higher layers in a CDMA system. In a method, packets are received from the HARQ entity by the re-ordering entity and missing packets among the received packets are detected. Packets may be transmitted in a sequential order based on transmission sequence numbers (TSNs) assigned to the packets, and missing packets may be detected based on the TSNs of the received packets. Delivery of received packets later than the missing packets are stalled because higher layers expect data in-order. A determination is thereafter made whether each missing packet is (1) subsequently received from the HARQ entity or (2) lost, by successively eliminating HARQ channels that may be used to send the missing packet. Received packets previously stalled by each missing packet are delivered after the missing packet is determined to be lost or received.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present Application for Patent is a Continuation and claims priorityto patent application Ser. No. 10/176,353 entitled “Improved DataDelivery in Conjunction with a Hybrid Automatic Retransmission Mechanismin CDMA Communication Systems” filed Jun. 19, 2002, now U.S. Pat. No.6,901,063, issued May 31, 2005, which claims the benefit of provisionalU.S. Application Ser. No. 60/380,408, entitled “A Method and Apparatusfor Stall Avoidance in a Communication System,” filed May 13, 2002, andassigned to the assignee hereof and hereby expressly incorporated byreference herein.

BACKGROUND

1. Field

The present invention relates generally to data communication, and morespecifically to techniques for improving the performance of datadelivery to higher layers in conjunction with a hybrid automaticretransmission (HARQ) mechanism in CDMA communication systems.

2. Background

Wireless communication systems are widely deployed to provide varioustypes of services such as voice, packet data, and so on. These systemsmay be multiple-access systems capable of supporting communication bymultiple users, and may be based on code division multiple access(CDMA), time division multiple access (TDMA), frequency divisionmultiple access (FDMA), or some other multiple access techniques. CDMAsystems may provide certain advantages over other types of system,including increased system capacity.

To improve the reliability of data transmission, some newer-generationCDMA systems employ a hybrid automatic retransmission (HARQ) mechanismthat can retransmit packets that have been incorrectly decoded by thereceiver. For example, in W-CDMA Release 5, the HARQ is included in aMedium Access Control (MAC)-hs sublayer that resides on top of thephysical layer. On the downlink, an HARQ entity at the transmitterprocesses data into packets that are assigned sequential transmissionsequence numbers (TSNs). These packets may then be transmitted insequential order based on their TSNs to the receiver.

At the receiver, a corresponding HARQ entity receives the packettransmissions and attempts to decode and recover each transmittedpacket. However, due to degradation in the packet transmissionsresulting from the radio link, some of the packets may not be decodedcorrectly (i.e., erased). When this occurs, a negative acknowledgment(NAK) is sent from the receiver back to the transmitter to initiate aretransmission of each erased packet.

The receiver HARQ entity is also tasked with providing the recoveredpackets (i.e., those decoded correctly) to higher layers. In W-CDMA, thehigher layers expect data in the proper order, as determined by the TSNsof the packets. However, with the HARQ mechanism, packets may berecovered out-of-order by the receiver HARQ entity due toretransmissions. As a result, a re-ordering entity is used at thereceiver to buffer and re-order the packets as they are recovered by thereceiver HARQ. The re-ordering entity would then provide the packets inthe proper order, as they become available, to higher layers.

If packets are recovered out of order by the receiver HARQ entity, thenthe re-ordering entity may “stall” or delay its delivery of therecovered packets to higher layers. In particular, the re-orderingentity would stall the delivery of data to higher layers wheneverpackets are detected to be missing, until either (1) the missing packetsare recovered by the receiver HARQ or (2) the re-ordering entity isconfident that the missing packets are lost and will not be recovered bythe receiver HARQ. If the second condition is true, then anotherretransmission mechanism at higher layers may be relied upon toretransmit the lost data.

A challenge arises in determining the proper amount of time to wait bythe re-ordering entity before declaring that the missing packets arelost and providing the already recovered packets to higher layers. Onegoal is to avoid stalling the delivery of data to higher layers, sincewaiting a long time or indefinitely for lost packets that will not berecovered is undesirable. A short wait time would be better for thisgoal. A conflicting goal is to minimize erroneous declarations of lostpackets, so that unnecessary retransmissions with long delays by higherlayers (if supported) or packet loss (if no retransmissions areperformed by higher layers) are minimized. A long wait time wouldprovide better assurance that the packets are indeed lost. This problemis commonly referred to in the art as “stall avoidance”.

There is therefore a need in the art for techniques to improve theperformance of stall avoidance in a CDMA system.

SUMMARY

Techniques are provided herein to mitigate the effects of missingpackets and improve stall avoidance performance. In particular, thesetechniques may be used to more effectively deal with situations in whichthe delivery of data to higher layers is stalled because of missingpayloads. These techniques make use of information available from theHARQ processes in order to better decide whether or not to deliver datato higher layers.

Various mechanisms are provided herein that may be used singly or incombination to improve stall avoidance performance. These mechanismsinclude (1) transmission of the priority of each packet on a controlchannel instead of with the packet, (2) maintenance of an inactivitytimer for each HARQ channel, (3) transmission of a flushing indicationto “flush” one or more HARQ channels, which may in turn result in databeing flushed by the re-ordering entity to higher layers, (4) formationof a set of candidate HARQ channels for each missing packet, which arechannels that may be used for the missing packet, (5) determination ofwhether or not a missing packet is lost based on activity or inactivitydetected on the HARQ channels in the candidate set. These mechanisms aredescribed in further detail below.

In an embodiment, a method is provided for delivering data recovered byan HARQ entity in proper order to higher layers in a CDMA communicationsystem. In accordance with the method, packets are received from theHARQ entity by the re-ordering entity and missing packets among thereceived packets are detected. Packets may be transmitted in asequential order based on transmission sequence numbers (TSNs) assignedto the packets, and missing packets may be detected based on the TSNs ofthe received packets. Delivery of received packets later than themissing packets is stalled because higher layers expect data in-order. Adetermination is thereafter made whether each missing packet is (1)subsequently received from the HARQ entity or (2) lost, by successivelyeliminating HARQ channels that may be used to send the missing packet.Received packets previously stalled by each missing packet are deliveredafter the missing packet is determined to be lost or received.

A set of candidate HARQ channels may be formed for each missing packet.The candidate set may include, for example, all HARQ channels that areactive at (or a short time after) the time the packet is detected to bemissing. A HARQ channel may be eliminated from the set if (1) it isinactive for a particular period of time, (2) a packet is recovered fromthe HARQ channel, (3) a new packet is detected to be sent on the HARQchannel, or (4) an indication to flush the HARQ channel is received. Aninactivity timer may be used for each HARQ channel to determine whetheror not the channel is inactive, and may be restarted whenever a packettransmission is received on the channel.

These techniques may be used for various CDMA systems such as a W-CDMAsystem that implements Release 5 or later.

Various aspects and embodiments of the invention are described infurther detail below. The invention further provides methods, programcodes, digital signal processors, receiver units, transmitter units,terminals, base stations, systems, and other apparatuses and elementsthat implement various aspects, embodiments, and features of theinvention, as described in further detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 is a diagram of a CDMA communication system;

FIG. 2 is a diagram of a layer structure defined by W-CDMA Release 5;

FIG. 3 is a diagram illustrating the data encapsulation performed by aNode B for transmission on the HS-DSCH for high-speed data packet access(HSDPA);

FIGS. 4A and 4B are diagrams of a MAC-hs entity defined by W-CDMARelease 5 for the UTRAN side and the UE side, respectively;

FIG. 5 is a diagram illustrating the timing relationship between variousdownlink and uplink physical channels used to implement HSDPA;

FIGS. 6A and 6B are diagrams graphically illustrating a windowmaintained for a particular priority queue and a window maintained bythe receiver re-ordering entity, respectively;

FIGS. 7A through 7D illustrate four data transmission scenarios wherebyvarious mechanisms are relied on to flush data from the re-orderingqueue to higher layers;

FIG. 8 is a flow diagram of a process performed by the transmitter HARQentity to send a packet on a particular HARQ channel;

FIGS. 9A and 9B show a flow diagram of a process performed by thereceiver HARQ entity to receive a packet on a particular HARQ channel;

FIG. 9C is a flow diagram of a process performed by the receiver HARQentity to maintain all of the inactivity timers for the HARQ channels;

FIG. 9D is a flow diagram of a process performed by the receiver HARQentity upon receiving a flushing indication on a control message;

FIG. 10 is a flow diagram of a process performed by the transmitterre-ordering entity for a particular priority queue;

FIGS. 11A and 11B show a flow diagram of a process performed by thereceiver re-ordering entity for a particular priority queue;

FIG. 11C shows a flow diagram of an embodiment of a process performed bythe receiver reordering entity whenever an indication is received that adelay timer has expired.

FIG. 11D shows a flow diagram of an embodiment of a process performed bythe receiver reordering entity for a completed transaction on aparticular HARQ channel.

FIG. 12 shows a flow diagram of an overall process performed by thereceiver re-ordering entity to receive packets from the HARQ entity anddeliver packets to higher layers; and

FIG. 13 is a block diagram of an embodiment of a Node B and a UE.

DETAILED DESCRIPTION

FIG. 1 is a diagram of a CDMA communication system 100 that mayimplement the techniques described herein for improving stall avoidance.System 100 includes a number of base stations 104 that communicate witha number of terminals 106 (only one base station and two terminals areshown in FIG. 1 for simplicity). A base station is also referred to as aNode B, a base transceiver system (BTS), an access point, or some otherterminology. The base stations may be part of a UMTS Radio AccessNetwork (UTRAN). A base station and/or its coverage area are also oftenreferred to as a cell, depending on the context in which the term isused.

A terminal is also referred to as a user equipment (UE), a mobilestation, a remote station, an access terminal, or some otherterminology. Each terminal may communicate with one or more basestations on the downlink and/or uplink at any given moment, depending onwhether or not the terminal is active, whether or not soft handover issupported for the data transmission, and whether or not the terminal isin soft handover. The downlink (i.e., forward link) refers totransmission from the base station to the terminal, and the uplink(i.e., reverse link) refers to transmission from the terminal to thebase station.

The techniques described herein for improving stall avoidanceperformance may be implemented in various CDMA communication systems.Thus, CDMA system 100 may implement one or more commonly known CDMAstandards such as W-CDMA, cdma2000, IS-856, IS-95, and others. Forclarity, various aspects, embodiments, and implementation details forimproving stall avoidance performance are described below for a CDMAsystem that supports W-CDMA Release 5. Using W-CDMA terminology, thebase station, terminal, and system controller are respectively referredto as Node B, UE, and RNC in the following description.

W-CDMA supports various types of services such as voice, packet data,and so on. In W-CDMA, data to be transmitted to a particular UE isprocessed as belonging to one or more transport channels. Thesetransport channels are then mapped to one or more physical channels (atthe physical layer) assigned to the UE. A physical channel is defined byvarious parameters (e.g., carrier frequency, scrambling code,channelization code(s), and so on).

W-CDMA Release 5 further supports high-speed downlink packet access(HSDPA), which is a set of transport/physical channels and proceduresdefined as part of the UTRAN that enable high-speed transmission of dataon the downlink. For HSDPA, data is processed in blocks that are thenmultiplexed onto a high-speed downlink shared channel (HS-DSCH), whichis a downlink transport channel. The HS-DSCH is then mapped to ahigh-speed physical downlink shared channel (HS-PDSCH) that may beshared by multiple UEs. For W-CDMA, each packet transmission on theHS-PDSCH spans a 2 msec time interval that is referred to as atransmission time interval (TTI).

The following transport and physical channels defined by W-CDMA arereferred to herein:

-   -   DPCH—dedicated physical channel    -   HS-DSCH—high-speed downlink shared channel    -   HS-SCCH—shared control physical channel for the HS-DSCH    -   HS-PDSCH—high-speed physical downlink shared channel    -   HS-DPCCH—high-speed dedicated physical control channel (on the        uplink)        The HS-PDSCH may be used to transmit data in a time and code        division multiplexed (TDM/CDM) manner for multiple UEs. The        control information for the HS-PDSCH, which includes various        parameters used to properly receive the HS-PDSCH, is transmitted        on an associated HS-SCCH. The HS-DPCCH is used to carry feedback        from the UEs to report correctly and incorrectly received (i.e.,        erased) packets.

FIG. 2 is a diagram of a layer structure 200 defined by W-CDMA Release5. Layer structure 200 includes a Radio Link Control (RLC) layer 210, aMedium Access Control (MAC) layer 220, and a physical layer 230. The RLClayer performs automatic retransmission (ARQ) of data and typicallyresides at the Radio Network Controller (RNC). Retransmission via theRLC layer is typically associated with long delays because of the longround trip time between the RNC and UE. In the RLC layer, data isprocessed as belonging to logical channels.

For W-CDMA Release 5, the MAC layer is further partitioned onto a MAC-dsublayer 222 and a MAC-hs sublayer 224. The MAC-d sublayer performs aset of functions that includes (1) mapping logical channels to commonand dedicated transport channels, (2) multiplexing one or more logicalchannels onto one transport channel (C/T MUX), (3)ciphering/deciphering, and so on. The MAC-d sublayer provides data flowsto the MAC-hs sublayer, with each data flow being associated withcertain scheduling attributes.

The MAC-hs sublayer performs specific functions related to HSDPA, asdescribed below. The MAC-hs sublayer further provides the interfacebetween the MAC-h sublayer and the physical layer.

The physical layer provides the mechanism for transmitting data for theMAC layer and signaling for higher layers.

These various layers and sublayers for W-CDMA are described in variousstandard documents, which are publicly available.

FIG. 3 is a diagram illustrating the data encapsulation performed by aNode B for transmission on the HS-DSCH. In W-CDMA, data to betransmitted on the downlink is provided by the RLC layer in RLC protocoldata units (RLC PDUs), each of which includes a sequence number (SN) anddata. The MAC-d sublayer receives the RLC PDUs for one or more logicalchannels and, for each RLC PDU, inserts a (C/T) field to form acorresponding MAC-d PDU. The C/T field identifies the logical channelassociated with the RLC PDU.

The MAC-hs sublayer receives the MAC-d PDUs and forms MAC-hs PDUs. ForW-CDMA Release 5, each MAC-d flow may include data for one or morelogical channels at the RLC layer, and each MAC-d PDU may be associatedwith a particular priority. Since data is transmitted based on priorityand available resources, data with different priorities is stored indifferent priority queues within the MAC-hs sublayer. Thereafter, datais retrieved from the proper priority queue, as needed, and furtherprocessed for transmission on the HS-DSCH.

To form a MAC-hs PDU, the MAC-hs sublayer first receives and seriallyconcatenates one or more MAC-d PDUs from a particular priority queue toform the payload for the MAC-hs PDU. Padding bits may be added asnecessary to fill out the payload. The MAC-hs sublayer then adds aheader with the payload to form the MAC-hs PDU.

For W-CDMA Release 5, the MAC-hs header includes (1) a size index ID(SID) field indicative of the length of each MAC-d PDU in the MAC-hsPDU, (2) an N field indicative of the number of MAC-d PDUs included inthe MAC-hs PDU, (3) a transmission sequence number (TSN) assigned to andused to uniquely identify the MAC-hs PDU, and (4) a Queue ID (QID) fieldindicative of the specific priority queue from which the MAC-d PDUsincluded in the MAC-hs PDU were retrieved. The TSN allows the UE toidentify MAC-hs PDUs that have been recovered and is used to provideMAC-d PDUs in-order to the RLC layer, which expects data to be deliveredto it in the correct sequence. A mechanism is also provided by W-CDMA toallow for the transmission of MAC-hs PDUs of different sizes within thesame packet, but this is not described herein for simplicity.

MAC-hs PDUs are generated on the fly as they are needed. Each MAC-hs PDUis transmitted in a 2 msec TTI, which is the transmission unit on theHS-DSCH. For simplicity, a MAC-hs PDU is referred to herein as a“packet”.

Control information is concurrently transmitted on the shared HS-SCCHalong with each packet transmission. This control information includes(1) an HARQ process ID (HID), (2) a New Data indicator, (3) informationidentifying the specific UE to which the control information and thecorresponding data transmission are intended, and (4) other informationnot described herein. The HID indicates the specific HARQ process usedfor the packet. Each packet may be transmitted and possiblyretransmitted one or more times until (1) the UTRAN receives an ACKfeedback on the HS-DPCCH for the packet, or (2) the transmitter decidesto abandon the transmission of the packet. Each packet is associatedwith a specific HARQ process, which is an instance of a stop and wait(SAW) protocol used to control the transmission/retransmission of thatpacket. Since three bits are defined for the HD, up to eight packettransactions may be pending at any given moment. The eight HARQprocesses may thus be viewed as eight “HARQ channels” that may be usedto transmit packets, with each HARQ channel being associated with andidentified by a specific HID value.

The New Data indicator is used to indicate the transmission of a newpacket on a particular HARQ channel. To improve decoding performance,the UE typically (soft) combines all received transmissions for the samepacket prior to decoding. The New Data indicator informs the UE that thecurrent transmission is for a new packet and that all prior receivedtransmissions for the same HARQ channel (which are for a prior packet)should be purged. The New Data indicator is a single bit value thattoggles between “0” and “1” for consecutive packets transmitted on thesame HARQ channel, and is effectively a 1-bit sequence number for thepackets transmitted on the HARQ channel. The UE can thus detect a newpacket by observing the New Data indicator toggles. The New Dataindicator is also referred to herein as the “color” bit.

FIG. 4A is a diagram of a MAC-hs entity 224 a defined by W-CDMA Release5 for the UTRAN side. There is one MAC-hs entity in the UTRAN for eachcell that supports HS-DSCH transmission. The MAC-hs entity handles datatransmitted on the HS-DSCH and further manages physical resourcesallocation for HSDPA.

The UTRAN MAC-hs entity includes a scheduling/priority handling entity410, an HARQ entity 420, and a TFRC entity 430. The scheduling/priorityhandling entity manages the data flows from the MAC-d entity accordingto their priorities, determines the TSN and priority queue for eachpacket being processed, and determines the transmission/retransmissionof packets. The data flows from the MAC-d entity may include data withdifferent priorities, which would then be placed in different priorityqueues. Data would thereafter be retrieved from the proper priorityqueue, based on priority and resource availability, and furtherprocessed for transmission/retransmission on the HS-DSCH.

One HARQ entity is provided to handle HARQ functionality for each UE.The HARQ entity performs transmission and (if necessary) retransmissionsof packets to ensure reliable delivery of these packets to the UE.Retransmissions of packets are performed based on feedback from the UE.This feedback is in the form of an acknowledgment (ACK) to indicatesuccessful decoding of a packet or a negative acknowledgment (NAK) toindicate an unsuccessful decoding of the packet.

The TFRC entity selects the appropriate transport format and resourcesfor the data to be transmitted on the HS-DSCH.

FIG. 4B is a diagram of a MAC-hs entity 224 b defined by W-CDMA Release5 for the UE side. The MAC-hs entity handles HSDPA specific function andincludes an HARQ entity 440, a re-ordering queue distribution entity450, and one set of re-ordering buffer 462, re-ordering entity 464, andde-assembly entity 466 for each Queue ID configured at the UE. Onere-ordering buffer is thus provided for and is associated with eachpriority queue used for the UE.

The UE HARQ entity handles all tasks required for HARQ (e.g., generatesthe required ACK/NAK for each received packet transmission). There-ordering queue distribution entity provides recovered packets to theproper re-ordering buffer based on the Queue ID sent for the packet.

The reordering entity for each re-ordering buffer reorders the recoveredpackets in the buffer according to the TSN assigned to each packet. Eachpriority queue is associated with its own sequence of TSNs. Thereordering entity then provides packets with consecutive TSNs, as theyare recovered, to the de-assembly entity. The packets are not deliveredto the de-assembly entity (i.e., “stalled”) if packets with lower TSNsare missing.

The de-assembly entity associated with each re-ordering bufferde-assembles the packets provided to it. The de-assembly is performed byremoving the header in each packet to obtain the MAC-hs payload (seeFIG. 3), extracting the MAC-d PDUs included the MAC-hs payload, anddiscarding padding bits (if any). The de-assembly entity then providesthe MAC-d PDUs to higher layers via the MAC-d sublayer.

W-CDMA Release 5 allows for a number of re-ordering entities and anumber of HARQ processes (or HARQ channels) to be operatingconcurrently. Each re-ordering entity processes data for one specificpriority queue and employs one re-ordering buffer for this task. Thereis thus a one-to-one correspondence between re-ordering entity, priorityqueue, and re-ordering buffer. The HARQ channels are standard stop andwait entities, and each HARQ channel can carry data meant for any of thepriority queues (or re-ordering buffers).

FIG. 5 is a diagram illustrating the timing relationship between variousdownlink and uplink physical channels used to implement HSDPA. Thetiming relationship shown in FIG. 5 is for a specific UE designated toreceive HSDPA transmission.

The uplink DPCCH is used by the UE to send signaling for the uplinkDPCH. The timing of the uplink DPCCH is used as a reference, and thetiming for the other physical channels is provided relative to that ofthe uplink DPCCH.

As shown in FIG. 5, a packet is transmitted to the UE in subframe 512 onthe HS-DPSCH. Each subframe spans one 2-msec slot. The start of subframe512 occurs some amount of time after time T1, which is the start of aslot on the uplink DPCCH. The packet is transmitted to the designatedUE, which receives and attempts to recover the packet. Based on theoutcome of the decoding process, the UE reports back one of thefollowing: (1) an ACK to indicate that the packet has been receivedcorrectly, (2) a NAK to indicate that the packet has been received inerror (i.e., erased), or (3) nothing (i.e., a discontinuous transmission(DTX) bit) if it failed to detect (missed) the corresponding HS-SCCH.This feedback information is transmitted from the UE in a designatedsubframe 514 on the uplink HS-DPCCH. Subframe 514 starts at time T2,which is defined to be 7.5 slots plus a delay of τ_(x) (which is a valuebetween 0 to 255 chips) from the end of the corresponding subframe 512.The delay τ_(x) is defined such that the elapsed time, τ_(y), betweenthe start of the slot on the uplink DPCCH (T1) and the start of subframe514 on the uplink HS-DPCCH (T2) is 256×m, where m is an integer.

The HSDPA design assumptions for the transmission of control informationon downlink HS-SCCH and the uplink HS-DPCCH are as follows:

HS-SCCH (Downlink)

-   -   Probability {Miss HS-SCCH}≦10⁻²    -   Probability {False alarm}≦10⁻⁴

HS-DPCCH (Uplink)

-   -   Probability {ACK→NAK}≦10⁻²    -   Probability {NAK→ACK}≦10⁻⁴    -   Probability {DTX→ACK}≦10⁻²        The above states that for the HS-SCCH on the downlink (1) the        probability of missing a control message accompanying a packet        transaction needs to be less than or equal to 10⁻² and (2) the        probability of mis-detecting a control message sent to another        UE as one being sent to the UE needs to be less than or equal to        10⁻⁴. For the HS-DPCCH on the uplink (1) the probability of an        ACK transmitted by the UE being received as a NAK by the Node B        needs to be less than or equal to 10⁻² (2) the probability of a        NAK transmitted by the UE being received as an ACK by the Node B        needs to be less than or equal to 10⁻⁴, and (3) the probability        of a DTX bit transmitted by the UE being received as an ACK by        the Node B needs to be less than or equal to 10⁻².

In some channel conditions, especially in cases where the serving Node Bfor a particular UE is not the one with the best uplink (which may occuroften since handing off from one Node B to another is slow for HSDPA),it may be difficult to achieve the ACK/NAK probability of error notedabove.

A NAK to ACK error for a given packet results in the transmitterassuming that the packet has been correctly recovered by the receiver.The transmitter can then discard this packet and initiate thetransmission of another packet on the same HARQ channel. Therefore, theNAK to ACK error results in a lost packet at the MAC layer. A higherprobability of NAK to ACK error corresponds to higher occurrence ofmissing packets at the MAC layer. This in turn leads to higherprobability of stalling by the re-ordering entity and moreretransmissions required at the RLC layer.

The MAC layer needs to guarantee delivery of data in-order to higherlayers. Since the HARQ mechanism using multiple HARQ channels may resultin data being recovered out of sequence by the UE, a re-orderingsublayer was added in the MAC layer in W-CDMA Release 5. The re-orderingsublayer buffers packets as they are recovered, re-orders these packets,and delivers consecutive packets (as determined by their TSNs) to higherlayers. If the re-ordering sublayer detects missing packets, based ongaps or holes in the TSNs of the recovered packets, then it holds off on(i.e., stalls) the delivery of all packets with TSNs later than the TSNof the earliest missing packet. When the missing packets are finallyrecovered, the re-ordering sublayer would then provide these newlyrecovered packets as well as any prior recovered packets that have beenstalled.

Three “stall avoidance” mechanisms are provided by W-CDMA Release 5 toallow for practical implementations and to avoid situations where there-ordering entity waits indefinitely for data that is notretransmitted. These stall avoidance mechanisms include:

-   -   Window-based scheme    -   Timer-based scheme    -   HARQ activity scheme        Each of these schemes is briefly described below.

Window-Based Scheme

Since each packet is tagged with a specific TSN, the recovered packetsmay be assembled in the proper sequence at the UE. Although the packetsmay be initially transmitted in sequential order by the Node B, thesepackets may be recovered out of order because a variable number ofretransmissions may be required for each packet.

FIG. 6A is a diagram graphically illustrating the window maintained fora particular priority queue. The data for this priority queue istransmitted in packets that are identified by a 6-bit TSN. The TSNnumber space is 2⁶=64 (i.e., from 0 through 63). To resolve ambiguity inthe TSN number space caused by the fact that the TSN field has a finitesize, the receiver may use a window. The size of this window istypically set at less than half of the TSN number space (i.e., <32) andmay be set as small as 8 to 16. Since the window size is smaller thanthe TSN number space, the order of the packets within the window isunambiguous. In determining the size of the window, there is a tradeoff.If the window is small, the stall avoidance performance at the receiverincreases and the receiver buffer size requirement is reduced. However,the stall probability at the transmitter or the probability of needingto interrupt retransmissions (depending on the transmission strategy) isincreased.

The window is advanced forward as new packets are received. For thereceiver, the leading edge of the window may be set equal to the“latest” TSN of all recovered packets. Packets toward the left of thewindow have successively “earlier” TSNs. Since the TSN value can wraparound, the latest TSN value may actually be smaller than an earlier TSNwhenever the TSN wraps around. Missing packets with TSNs earlier thanthe trailing edge of the window may be assumed to be lost (i.e., notretransmitted). Thus, as the window is advanced forward, packets earlierthan the trailing window edge are “flushed” and sent to higher layers.

This window mechanism may therefore be used by the transmitter to flushout missing packets at the receiver. However, since the size of thewindow would need to be large to allow for a large number ofretransmissions, a large amount of data would be needed to flush out themissing packets. Consequently, the window-based scheme is marginallyeffective at the end of data bursts, which are frequent in the case ofbursty closed loop traffic such as what is generated by browsing.

Timer-Based Scheme

In order to address the limitations of the window-based scheme, atimer-based mechanism was also introduced in W-CDMA Release 5. For thetimer-based scheme, each time a missing packet stalls the delivery ofpackets to higher layers at the receiver, a “long” timer is started. Ifno other missing packets are thereafter detected then, once the longtimer expires, the missing packet is assumed to have been recovered, andall packets stalled by this missing packet are then delivered to higherlayers. This mechanism requires the maintenance of one long timer perre-ordering queue (or a maximum of eight long timers for the eightre-ordering queues defined in W-CDMA Release 5).

To ensure proper HARQ operation, the long timer needs to be set longerthan the longest amount of time it takes to complete all retransmissionsfor a given packet. A large number of retransmissions may need to beperformed to recover the missing packet. Moreover, in a system thatasynchronously schedules retransmissions and where the amount ofresources (e.g., as quantified by channelization codes and transmitpower) available for HSDPA can change dynamically, the amount of time ittakes to complete all retransmissions for a missing packet can varywidely. Consequently, the value of this timer would need to be long.Otherwise, the retransmissions for the missing packet may be prematurelyterminated by the expiration of the timer, in which case the missingpacket would need to be retransmitted by higher layers, which is highlyundesirable. The re-ordering entity may need to wait a significantamount of time for the long timer to expire or until all theretransmissions for the missing payload are completed.

In addition to the large value for the long timer, if several packetswithin the window are detected as missing, then the timers for thesemissing packets are effectively cascaded (i.e., the long timer isrestarted whenever a new missing packet is detected). This may result ineven longer delays in delivering the missing payloads to higher layers(with the longest possible delay being two times the value of the longtimer in the worse case).

HARQ Activity Scheme

The third scheme to avoid stalling the delivery of recovered packets tohigher layers is to detect activity on the HARQ channels. When nopackets are expected on any of the HARQ channels (i.e., all of theprevious packet transactions are completed), then the data in allre-ordering queues can be delivered by the re-ordering entities tohigher layers. This mechanism has a few shortcomings. First, this schemerequires that no packet transaction is pending on any of the HARQchannels in order to be able to flush the packets to higher layers.Second, the receiver “marks off” a HARQ channel only if the packettransaction on that channel is completed. Since the receiver may waitindefinitely for a packet to be recovered on a given HARQ channel (e.g.,if the transmitter abandons the packet transaction), the re-orderingqueues may never be flushed. Third, if a control message is missed(i.e., not detected by the receiver), then it is possible that thepacket associated with this control message will be discarded by there-ordering entity, if it is subsequently recovered. This would be thecase if another packet with a later TSN is recovered and provided to there-ordering entity before the packet with the missed control message isretransmitted and the control channel is successfully decoded.

Techniques are provided herein to mitigate the effects of missingpackets and improve stall avoidance performance. In particular, thesetechniques may be used to more effectively deal with situations in whichthe delivery of data by the MAC-hs sublayer to higher layers is stalledbecause of missing payloads. These techniques make use of informationavailable from the HARQ processes in order to better decide whether ornot to deliver data to higher layers.

The following mechanisms may be used to improve stall avoidanceperformance:

-   -   Transmission of the Queue ID on the HS-SCCH instead of with the        payload.    -   Maintenance of an inactivity timer for each HARQ channel.    -   Transmission of a flushing indication to “flush” one or more        HARQ channels, which may in turn result in data being flushed by        the re-ordering entity to higher layers.    -   Formation of a set of candidate HARQ channels for each missing        packet, which are channels that may be used to send the missing        packet. A delay timer may be used for the candidate set        formation.    -   Detection of activity on the HARQ channels to determine whether        or not missing packets are lost.

Each of these mechanisms is described in further detail below.

The following terminology is used in the following description:

-   -   Packet transaction—a transmission and zero or more        retransmissions of a particular packet on a particular HARQ        channel.    -   Pending transaction—a packet transaction in which one or more        additional retransmissions are expected for the packet.    -   Completed transaction—a packet transaction in which no        additional retransmissions are expected for the packet.    -   Missing packet—a packet that is not recovered by the receiver        and has a TSN earlier than that of another packet that has been        recovered (a missing packet may still be in the process of being        retransmitted or may have been discarded by the transmitter).    -   Recovered packet—a packet decoded correctly by the receiver.    -   Received packet—this term has two meanings depending on which        entity is referred to. For the HARQ entity: a packet        transmission received on a particular HARQ channel, which may or        may not be decoded correctly. For the re-ordering entity: a        recovered packet that is received from the HARQ entity but not        yet delivered to the upper layers.    -   Active HARQ channel—a HARQ channel in which the packet        transaction is pending and the next transmission received on the        channel should be for a retransmission of the current packet.    -   Inactive HARQ channel—a HARQ channel in which the packet        transaction is completed and the next transmission received on        the channel should be for a new packet    -   Candidate HARQ channel—a HARQ channel that may be used to send a        packet detected to be missing.

Transmission of Queue ID on the Control Channel

In W-CDMA Release 5, the Queue ID that identifies the specific priorityqueue for a packet is transmitted as part of the header for that packet(see FIG. 3). Therefore, the priority queue to which the packet payloadbelongs can only be ascertained after the packet has been recovered. Asa consequence, it is not possible to determine the priority queueassociated with each missing packet since the packet has not beenrecovered.

If a packet is missing and the priority queue to which it belongs cannotbe ascertained, then data delivery may be stalled for all re-orderingentities. This can degrade performance.

In an aspect, the priority queue for each packet is sent on the controlmessage along with the packet transmission. A Queue ID field may beincluded in the control message, as shown by the dashed box in FIG. 3.By transmitting the Queue ID on the control channel, it would bepossible to identify the priority queue for each packet for which theassociated control message is correctly detected by the receiver,regardless of whether the packet itself is decoded correctly or inerror. The information identifying the priority queue for each suchpacket may be used in conjunction with other mechanisms described belowto further improve stall avoidance performance. For example, when usedin conjunction with a mechanism described below, by identifying thepriority queues for each such packet, it is possible to determine thepriority queues that may be flushed to higher layers. This way, eachsuch packet only affects the re-ordering entity associated with thepriority queue for that packet and not the other re-ordering entities.Stall avoidance performance may therefore be improved.

Inactivity Timer for HARQ Channel

Each HARQ channel may be used to transmit one packet at any givenmoment. The packet is transmitted and possibly retransmitted one or moretimes on the HARQ channel until either (1) the transmitter receives anACK for the packet or (2) the transmitter gives up on the transmissionof the packet. In either case, the transmitter may thereafter send a newpacket on the same HARQ channel and would indicate this by flipping theNew Data indicator.

At the receiver, the packet transaction on a particular HARQ channel isdeemed pending until (1) the packet is recovered correctly from the HARQchannel by the receiver, or (2) the receiver detects the transmission ofa new packet on the HARQ channel (based on the New Data indicator in thecontrol channel), since the transmitter would not send the new packetunless it decides to stop the transmissions of the prior packet.

At the receiver, new data will “flush” the pending data in the receiverwindow, which may have been discarded by the transmitter for one reasonor other. For example, if there is no more data to be sent for priorityqueue A but there is still new data to be sent for priority queue B,then the data for priority queue B may be sent on the same HARQ channelspreviously used for priority queue A. In this case, the data forpriority queue B would effectively “over-write” the data for priorityqueue A. The toggling of the New Data indicator for each HARQ channelallows the receiver to ascertain when the prior packet is beingdiscarded by the transmitter.

However, if there is no more data to transmit, then there may be noactivity on any of the HARQ channels. Without new activity, it is notpossible for the UE to ascertain whether a given packet has beendiscarded by the network or that a retransmission for the packet isforthcoming. For each HARQ channel that is waiting for a packet that hasbeen discarded by the transmitter and for which no new packet has beensent, the re-ordering entity associated with this HARQ channel will haveto wait until the long timer maintained for the re-ordering queueelapses before it can deliver the available data to higher layers. TheHARQ process will itself wait indefinitely for the transmission of a newpacket or a retransmission of the current packet on the HARQ channel.

In another aspect, an “inactivity” timer may be maintained for eachactive HARQ channel to avoid the situation whereby the HARQ entity waitsindefinitely for a retransmission of a packet that has been discarded bythe transmitter. In an embodiment, the inactivity timer monitorsactivity on HARQ channel based on control messages received on thecontrol channel for that HARQ channel. In one implementation, each timea new control message is received on the control channel for aparticular active HARQ channel, the inactivity timer for that channel isrestarted. If the inactivity timer elapses before another new controlmessage is received for the HARQ channel, then the channel is deemed tobe inactive.

A major advantage of using an inactivity timer for each HARQ channel isthat it does not need to be as long as the long timer used for eachre-ordering buffer. This is because the inactivity timer only needs tocover the maximum amount of time expected to take to receive a controlmessage for an active HARQ channel (or two control messages, just incase the first one was missed). Since the probability of miss for thecontrol channel is in the order of 10⁻², the probability of missing twocontrol channel transmissions in a row would be in the order of 10⁻⁴.Therefore, if the timer is set to the maximum time needed to perform tworetransmissions, then the probability of erroneously discarding a packetstill being transmitted would be approximately the same as the desiredprobability of NAK to ACK error, which is desirable since the two haveessentially the same effect. In contrast, the long timer needs to belong enough to handle the maximum number of retransmissions for amissing packet (and not just two control message transmissions).

A local variable CurrNewData may be maintained for each HARQ channel andset to the New Data indicator received in the most recent transmissionon the channel. If the HARQ channel is deemed to be inactive, then thenext transmission on the channel is expected to be for a new packet, inwhich case the New Data indicator for this transmission will bedifferent from the CurrNewData value. However, if the New Data indicatorfor the new transmission is the same as the CurrNewData value, then itmay be assumed that the same packet is being sent (e.g., due to an ACKto NAK error), in which case the transmission may be discarded and anACK may be sent back to the transmitter.

Flushing Indication for HARQ channels

In yet another aspect, a flushing indication may be transmitted on thecontrol channel and used to direct the HARQ entity at the UE to flushone or more HARQ channels. A flushed HARQ channel denotes that thepending transaction on the channel is completed. The re-ordering entitywaiting on this HARQ channel may then perform the appropriate actionsbased on this information, as described below.

Various flushing indication may be sent to the UE in various manners.For example, the flushing indication may be sent in a control messageusing a reserved value in a field used to indicate code set or a fieldused to indicate transport block size. If the UE receives a flushingindication, it would not attempt to decode a packet. The reason for thisis described below. Each flushed HARQ channel may then be put in anInactive state to indicate that no additional retransmissions areexpected to be received on the channel.

One or more HARQ channels may be flushed based on a single flushingindication. In a first embodiment, the flushing indication only flushesthe specific HARQ channel for which it is sent, which may be identifiedby the HID field in the control message. For this embodiment, multipleflushing indications may be sent if multiple HARQ channels are to beflushed. In a second embodiment, the flushing indication flushes allHARQ channels. This embodiment reduces the number of transmissions forflushing indications. However, the applicability of the flushingindication would also be reduced to the case where no data needs to besent on any of the HARQ channels for any of the re-ordering queues. In athird embodiment, the flushing indication flushes all HARQ channelsexpecting data for a particular priority queue, which may be indicatedin the Queue ID field included in the same control message used to sendthe flushing indication. This embodiment may be used to flush all HARQchannels for a particular priority queue after the transmission of allthe data in the traffic burst meant for that priority queue has beencompleted.

The transmission of a flushing indication does not require significantresources and may be used to terminate early the inactivity timermaintained for a particular HARQ channel. Typically, the system knowswhich UEs have increased risk of missing packets in their re-orderingbuffers. For example, UEs with better uplink to a cell other than theserving cell or high frame error rates (FERs) on the DPCH are morelikely to have missing packets. For these UEs, a flushing indication maythen be sent upon completion of the transmission of the traffic burstfor each priority queue.

Detection of Activity on HARQ Channel/Delay Timer for Missing Packet

If the first transmissions of the packets occur in sequential orderbased on their TSNs, then missing packets may be identified by the TSNsof the recovered packets. In particular, a packet may be deemed as beingmissing if another packet with a later TSN is recovered first. (A laterTSN may be smaller in value than an earlier TSN, when the TSN valuewraps around.) In this case, the missing packet with an earlier TSN maybe assumed to be in transmission.

At the moment a packet is detected to be missing, a set of candidateHARQ channels on which the missing packet may be sent can be identified.Thereafter, activities on the candidate HARQ channels may be monitoredto determine whether or not any of these channels may have been the oneused to send the missing packet. The candidate HARQ channels may thus besuccessively removed from the set, as described below. A missing packetis deemed to be lost if all candidate HARQ channels are removed and theset is empty. Appropriate action may then be taken by the re-orderingentity.

The HARQ channels to be included in the candidate set may be selected invarious manners, which may be dependent on the available information. Ina first embodiment, the candidate set is formed upon detecting a missingpacket and would include all HARQ channels that may be used for packettransmission, except for the HARQ channel for the recovered packet thatwas used to detect the missing packet.

In a second embodiment, the candidate set for a missing packet isdefined to include all active HARQ channels at the time the missingpacket is detected. The snapshot of the candidate HARQ channels at thistime would be accurate if at least one control message for the missingpacket is received, since that control message would put the HARQchannel corresponding to the missing packet in the active state, and thechannel would then be included in the candidate set for the missingpacket.

However, this snapshot would not be accurate if all control messages forthe HARQ channel used to send the missing packet were missed by thereceiver. For example, if a control message for the first transmissionof packet P1 sent on HARQ channel H1 is missed, then this channel wouldremain in the Inactive state. Thereafter, if another packet P2 for thesame priority queue is sent on another HARQ channel and is decodedcorrectly (before packet P1 is retransmitted on HARQ channel H1), thenpacket P1 would be detected to be missing. However, the candidate setwould not include HARQ channel H1 since it is inactive when the snapshotof the set is taken after packet P2 was recovered. The likelihood ofthese events occurring may be low, and the impact would be that packetP1 would be discarded by the re-ordering entity when it is finallyrecovered.

In a third embodiment, which avoids the problem described above, thecandidate set for a missing packet is formed some amount of time afterthe missing packet was detected. This delay is selected to be longenough to ensure that at least one control message will be received forthe missing packet before the candidate set is formed for the missingpacket. A “delay” timer (denoted herein as TM2) may be used to keeptrack of the amount of time to wait before taking the snapshot of thecandidate set.

Based on the specified reliability for the control channel, which is10⁻², the delay timer would only need be long enough to receive oneadditional control message transmission. If the delay timer is used,then the receiver would in effect need to miss two consecutive controlmessage transmissions in order to form an inaccurate candidate set, andthus lose the packet. Based on a probability of miss of 10⁻² for thecontrol channel, two consecutive control channel misses would occur witha probability of 10⁻⁴, which is deemed acceptable. A longer value forthe delay timer may degrade performance rather than affect theunderlying scheme.

In a fourth embodiment, a candidate set is initially formed for eachmissing packet at the time the missing packet is detected, and wouldinclude all HARQ channels except for the HARQ channel of the recoveredpacket used to detect the missing packet (same as the first embodiment).However, a delay timer is also started. The candidate HARQ channels inthe set may thereafter be removed if it is subsequently determined thatthe channel cannot be used to send the missing packet. At the expirationof the delay timer, the candidate set is modified and all HARQ channelsthat are not active at this time are removed from the set. The modifiedcandidate set is a subset of the initial candidate set. For the fourthembodiment, the delay timer is used to catch HARQ channels for which allcontrol messages have been missed previously by the receiver, similar tothe third embodiment described above. However, the operation of thedelay timer does not affect or impair the removal of HARQ channels fromthe initial formed candidate set (e.g., HARQ channels for which packetswith later TSNs have been recovered).

For the embodiments that make use of the delay timer, this timer may beimplemented in various ways, as described in further detail below.

If the Queue ID is also sent on the control channel and at least onecontrol message is received for the missing packet, then the candidateset for the missing packet would only need to include the HARQ channelsused for this priority queue. Performance may be enhanced since thenumber of candidate HARQ channels may be reduced.

The delay timer and flushing indication mechanisms can help put the HARQchannels into an inactive state by the time the candidate set is formed.For example, the inactivity timer for a given HARQ channel may elapseduring the time the delay timer is active, in which case this HARQchannel would not be included in the candidate set. These mechanisms maythus restrict the set of candidate HARQ channels, which may improve theperformance of the stall avoidance mechanism.

For all embodiments used to form the candidate set for a missing packet,the candidate HARQ channels are thereafter removed from the set if it issubsequently determined that they cannot be used to send the missingpacket. In particular, a candidate HARQ channel is removed from the setif the pending transaction on the channel becomes completed.

In an embodiment, a packet transaction on an HARQ channel is deemed tobe completed if any one of the followings conditions occurs: (1) thepacket is recovered from the HARQ channel, (2) the HARQ channel isactive and a new packet is detected to have been sent on the channel,(3) the inactivity timer for the HARQ channel expires, or (4) a flushingindication is received for the HARQ channel. Condition (1) results inthe recovery of the missing packet or the recovery of a packet that islater than the missing packet. Condition (2) may be detected byobserving the New Data indicator changes and may occur, for example, ifthe transmitter decides to abandon the prior packet and instead send anew packet on the HARQ channel. Conditions (1) and (2) also assume thatinitial transmissions are always performed in sequence and that a newpacket is not transmitted on the same HARQ channel until the pendingtransaction is completed.

For a given missing packet, each HARQ channel in the associatedcandidate set may be removed if any of the four conditions describedabove occurs. When the candidate set is empty, then the missing packetis assumed to be lost (i.e., will not be recovered by the receiver).Appropriate action may then be performed. For example, all recoveredpackets stalled because of this missing packet may now be delivered tohigher layers.

As noted above, the transmission of the Queue ID on the control channelmay be used in conjunction with other mechanisms described above toimprove performance. In particular, the Queue ID on the control channelmay (1) reduce the number of candidate HARQ channels for a missingpacket, (2) allow for possible tailoring of the inactivity timer to thepriority queue, and (3) allow use of the flush indication even whenother re-ordering entities are in the middle of transmissions.

In the following description, the candidate set is formed after theexpiration of the delay timer, which is started when a missing packet isdetected.

Example Transmissions

The various mechanisms described above to improve stall avoidanceperformance is described below for some example transmissions. For theseexamples, the NAK/ACK feedback on the HS-DPCCH is shown aligned with thetime of the packet transmission that it relates to (for simplicity). The“transmitted” feedback values are those sent by the UE on the uplink,and the “received” feedback values are those detected by the Node B. Thefirst transmissions for the packets are in sequential order based on theTSNs of the packets. Thus, missing packets may be determined based onthe TSNs of the packets recovered by the UE.

In the following examples, a delay timer (TM2) is set when a packet isdetected to be missing. A set of candidate HARQ channels for the missingpacket is determined after the delay timer expires.

FIG. 7A illustrates a case where the control channel is received and theNew Data indicator in the control message is relied on to flush datafrom the re-ordering queue to higher layers.

At time T1, a packet was received on HARQ channel H1 but not decodedcorrectly. For this packet transmission, the receiver sends a NAKfeedback, which is erroneously received by the transmitter as an ACK.The state of HARQ channel H1 is set to Active and the HARQ entityrestarts the inactivity timer (TM1) for this channel.

At time T2, a packet with TSNx was received on HARQ channel H2 anddecoded correctly, and an ACK feedback is sent for this packettransmission. The state of HARQ channel H2 is set to Inactive. Therecovered packet is then sent to the re-ordering entity for the priorityqueue of this packet. The re-ordering entity is able to detect that apacket with TSNx−1 is missing based on TSNx of the packet it justreceived. A delay timer (TM2) is then started for the missing packet.The recovered packet with TSNx is stalled because of the missing packet.

At time T3, a packet was received on HARQ channel H3 but not decodedcorrectly, and a NAK feedback is sent for this packet transmission. Thestate of HARQ channel H3 is set to Active, and the HARQ entity restartsthe inactivity timer for this channel.

At time T4, the delay timer for the missing packet expires, and the setof candidate HARQ channels for the missing packet is determined. Thecandidate set for the missing packet includes all HARQ channels that arein the Active state at the expiration of the delay timer and which maybe used to send the missing packet. The candidate set thus includes H1and H3.

At time T5, a packet with TSNx+1 was received on HARQ channel H3 anddecoded correctly, and an ACK feedback is sent for this packettransmission. The state of HARQ channel H3 is set to Inactive, and theHARQ entity restarts the inactivity timer for this channel. Therecovered packet with TSNx+1 is also stalled because of the missingpacket. Since the packet transaction for HARQ channel H3 is completedfor a packet that comes later than the missing packet, this channelcould not have been the one used to send the missing packet. H3 is thusremoved from the candidate set, which now includes only H1.

At time T6, a new packet was received on HARQ channel H1, with the NewData indicator toggled from D0 to D1. The new packet was sent by thetransmitter on this channel because it erroneously receives an ACK forthe prior packet transmission at time T1. This change in the New Dataindicator signifies that the pending packet transaction on HARQ channelH1 is completed, and that the missing packet will not be sent on thischannel. H1 is thus removed from the candidate set, which is now empty.The two stalled packets with TSNx and TSNx+1 are then delivered tohigher layers.

FIG. 7B illustrates a case where the control channel is received and theinactivity timer (TM1) is relied on to flush data from the re-orderingqueue to higher layers. The packet transmissions in FIG. 7B are similarto that shown in FIG. 7A, except that a packet transmission was notreceived at time T6. At time T7, the inactivity timer for HARQ channelH1 expires. This indicates that the missing packet is not expected to bereceived on this channel. H1 is thus removed from the candidate set,which then becomes empty. The two stalled packets with TSNx and TSNx+1are then delivered to higher layers.

FIG. 7C illustrates a case where the control channel is received and aflushing indication sent on the control channel is relied on to flushdata from the re-ordering queue to higher layers. The packettransmissions in FIG. 7C are similar to that shown in FIG. 7A, exceptthat a flushing indication (instead of a packet transmission) wasreceived at time T6. For this example, the flushing indication coversall HARQ channels used for the priority queue identified in the controlmessage. H1 and H3 would then be flushed because they are used for theidentified priority queue. The candidate set for the missing packetwould then become empty. The stalled packets with TSNx and TSNx+1 arethen delivered to higher layers.

FIG. 7D illustrates a case where the control channel is not received anda DTX to NAK error is received by the transmitter. FIG. 7D also shows asituation where the use of the delay timer allows for the correctdetermination of the candidate set for a missing packet, which wouldhave been lost otherwise.

At time T1, a packet was sent on HARQ channel H1 but the control channelwas not received (i.e., missed). The receiver does not know theexistence of this packet transmission and sends a DTX (i.e., nofeedback), which is erroneously received by the transmitter as a NAK.Because the receiver is not aware of the packet transmission, the stateof HARQ channel H1 remains set to Inactive and the inactivity timer forthis channel is not restarted.

At time T2, a packet with TSNx was received on HARQ channel H2 anddecoded correctly, and an ACK feedback is sent for this packettransmission. The state of HARQ channel H2 is set to Inactive, and theinactivity timer for this channel is restarted (not shown in FIG. 7D).The recovered packet is then sent to the re-ordering entity for thepriority queue of this packet. The re-ordering entity is able to detectthat a packet with TSNx−1 is missing based on the TSNx of the packet itjust received. A delay timer is then started for the missing packet.

At time T3, a packet retransmission was received on HARQ channel H1 forthe NAK detected by the transmitter at time T1, . This packet is notdecoded correctly, and a NAK feedback is sent for the packettransmission. The state of HARQ channel H1 is set to Active, and theHARQ entity restarts the inactivity timer for this channel (not shown inFIG. 7D).

At time T4, a new packet with TSNx+1 was received on HARQ channel H2with the New Data indicator changed to a new value (i.e., from D0 toD1). This packet was decoded correctly, and an ACK feedback is sent forthis packet transmission. The state of HARQ channel H2 is set toInactive, and the HARQ entity cancels the inactivity timer for thischannel.

At time T5, the delay timer for the missing packet expires. At thispoint, there is one Active HARQ channel, H1. The candidate set wouldthen include only HARQ channel H1.

As shown in this example, the use of the delay timer allows for thedetermination of the correct candidate set for the missing packet.Without the delay timer, the candidate set would be an empty set sincethe control message at time T1 for the packet with TSNx−1 was missed.With the delay timer, the second transmission at time T3 within thedelay timer window allows HARQ channel H1 to be included in thecandidate set.

At time T6, the missing packet with TSNx−1 was received on HARQ channelH1 and decoded correctly, and an ACK feedback is sent for this packettransmission. The packets with TSNx−1 and TSNx are then delivered tohigher layers.

At time T7, a packet retransmission was received on HARQ channel H2 forthe packet with TSNx+1, which was NAKed at time T4. This packet wasdecoded correctly and delivered by the re-ordering entity to higherlayers. An ACK feedback is also sent for the packet.

Specific Implementation

For clarity, a specific implementation of the processing performed bythe HARQ entities and the re-ordering entities at the transmitter andreceiver is described below. This implementation maintains a delay timerfor a missing packet to allow for a candidate set to be more accuratelyformed for the missing packet. However, this delay timer is not strictlynecessary as described above. If the delay timer is not used, then theresulting behavior is equivalent to setting the delay timer value to 0.

In the following implementation, it is assumed that the Queue ID is senton the control channel, and the priority queue of a given packet it isnot known to the HARQ entity until the packet is decoded correctly. Inthis case, when a packet transaction is completed, the HARQ entitynotifies all of the re-ordering entities since the lost packet couldhave been for any priority queue. Moreover, when the delay timerexpires, the re-ordering entity does not know which HARQ channels carrydata for it, and would therefore include all active HARQ channels in thecandidate set for the missing packet.

Transmitter HARQ

FIG. 8 is a flow diagram of an embodiment of a process 800 performed bythe transmitter HARQ entity to send a packet on a particular HARQchannel. For this embodiment, a local variable NewData is maintained foreach HARQ channel. This variable toggles for the first transmission of anew packet when the payload to be transmitted changes. This variable isinitialized to “1”.

Initially, a determination is made whether or not there is a packet tobe transmitted (step 812). If the answer is no, then the processproceeds to step 822. Otherwise, a determination is made whether or notthis is the first transmission of the packet (step 814). If the answeris again yes, then the NewData variable is toggled (i.e., set to “0” forthe first new packet), and the New Data indicator in the control messagefor the packet is also toggled since it is set to the NewData value(step 816). Otherwise, if the packet is being retransmitted, then step816 is skipped and the NewData variable is not toggled. The Queue ID inthe control message for the packet (if it is sent there) is set to thepriority queue of the packet being transmitted (step 818). The packetand the control message (which would include the HID, Queue ID, New Dataindicator, and so on) are then forwarded to the physical layer fortransmission (step 820).

In step 822, a determination is made whether or not an ACK was receivedfrom the UE for a current packet transmission (if any) on the HARQchannel. If the answer is yes, then the current packet being transmittedon this channel is discarded (step 824), and the scheduler is informedthat this HARQ channel is available to send another packet (step 826).After step 826, or if an ACK was not received in step 822, the processreturns to step 812.

Receiver HARQ

FIGS. 9A and 9B show a flow diagram of an embodiment of a process 900performed by the receiver HARQ entity to receive a packet on aparticular HARQ channel. Three local variables, CurrNewData,CurrQueueID, and CurrState, are maintained for each HARQ channel. TheCurrNewData variable holds the value of the New Data indicator for thecurrent transmission on the HARQ channel, and the CurrQueueID variableholds the value of the Queue ID for the current transmission. TheCurrState variable indicates the current state of the HARQ channel andis either Inactive or Active.

One inactivity timer is also maintained for each HARQ channel. In anembodiment, the inactivity timer is set long enough so that there is ahigh probability of two packet transmissions occurring on the HARQchannel before the inactivity timer expires. However, other values mayalso be used for the inactivity timer, and this is within the scope ofthe invention.

The variables for each HARQ channel are initialized by settingCurrNewData to “1” and CurrState to Inactive (step 910). A determinationis made whether or not a control message was received on the controlchannel for the UE (step 912). If the answer is no, then the processreturns to step 912 and waits. Otherwise, a determination is madewhether or not the control message includes a flushing indication (step914). If the answer is yes, then one or more HARQ channels are flushed,depending on the particular flushing scheme being implemented (step916). The flushing may be performed as described below in FIG. 9D. Aspart of the flushing processing, the re-ordering entity for each flushedHARQ channel is informed that the packet transaction is completed onthat channel. Since a control message with the flushing indication issent to only flush HARQ channels, and no packet is transmittedconcurrent with the control message, the process thereafter returns tostep 912 to wait for the next control message.

If the received control message was not sent to flush the HARQ channels,as determined in step 914, then it is one sent for a packet transmissionon the HS-DSCH. In that case, the particular HARQ channel used for thecurrent packet transmission is determined from the HID field in thecontrol message (step 922). The inactivity timer for this HARQ channelis then restarted (step 924). As described above, the inactivity timerfor the HARQ channel is restarted whenever a control message is receivedfor the channel, and if no activity is detected for the channel by thetime the inactivity timer expires, then the channel is deemed to beinactive and appropriate actions may be performed. The inactivity timeris used to avoid the situation whereby the HARQ entity waitsindefinitely for a packet transmission on a particular HARQ channel,which is not sent for any number of reasons. The processing to beperformed upon expiration of the inactivity timer is described below.

The current state of the HARQ channel is then determined based on theCurrState variable (step 926), and the processing to be performed forthe HARQ channel is dependent on the current state.

If the HARQ channel is in the Inactive state, indicating that the priorpacket transaction is completed, then the current transmission isexpected to be the first transmission for a new packet. In that case, adetermination is made whether or not the CurrNewData value is equal tothe New Data indicator in the control message for this packettransaction (step 930). If they are the same, indicating that thecurrent transmission is not for a new packet, then the received packetis discarded (step 932), an ACK is sent back to the transmitter (step934), and the process returns to step 912 to wait for the next controlmessage. The prior packet may have been sent, for example, if thereceiver sends an ACK for the prior packet transmission but thetransmitter erroneously receives a NAK instead and retransmits the priorpacket.

Otherwise, if the CurrNewData value is not equal to the New Dataindicator, indicating that the current transmission is for a new packet,then the variables for the HARQ channel are updated by setting CurrStateto Active (step 942), CurrNewData to the New Data indicator in thecontrol message (step 944), and CurrQueueID to the Queue ID value in thecontrol message (if it is sent there) (step 946). The new packetreceived on the HS-DSCH is then stored in a soft buffer used for thepriority queue identified by the CurrQueueID value (step 948). Theprocess then proceeds to step 958.

Back in step 926, if the HARQ channel is in the Active state, then thecurrent transmission is expected to be a retransmission for the currentpacket, since this transaction is still pending. In that case, adetermination is made whether or not the CurrNewData value is equal tothe New Data indicator in the control message (step 950). If they arethe same, indicating that the current transmission is indeed aretransmission, then the received packet is combined with priortransmissions of the packet (step 952) and the process then proceeds tostep 958.

Otherwise, if the CurrNewData value is not equal to the New Dataindicator as determined in step 950, then the current transmission isfor a new packet. The new packet may have been sent, for example, if thetransmitter decided to abandon the pending transaction before it iscompleted or erroneously receives an ACK for a transmitted NAK. In thatcase, the prior packet in the soft buffer is purged (step 954). If thepriority queue for the prior packet is known (e.g., as identified by theCurrQueueID value, which may be obtained from the Queue ID included inthe control message), then the re-ordering entity for this priorityqueue is informed that the transaction for the prior packet is completed(step 956). If the priority queue of the prior packet is not known(e.g., not sent on the control message), then all re-ordering entitiesmay be informed of the completed transaction on this HARQ channel. Thevariables for the HARQ channel are then updated by setting CurrNewDatato the New Data indicator in the control message (step 944) and settingCurrQueueID to the Queue ID value in the control message (if it is sentthere) (step 946). The new packet received on the HS-DSCH is then storedin the soft buffer (step 948), which was just purged of the priorpacket. The process then proceeds to step 958.

In step 958, the packet just received, which may have been combined withprior transmissions (if any) received for the packet, is then decoded toattempt to recover the packet. If the packet is not recovered, asdetermined in step 960, then a NAK feedback is sent to the transmitter(step 962), and the process returns to step 912. Otherwise, if thepacket was successfully recovered, then an ACK feedback is sent (step964), the current state of the HARQ channel is set to Inactive toindicate that the current packet transaction is completed and that noadditional transmissions are expected on this HARQ channel (step 966),and the recovered packet is sent to the re-ordering entity for thepriority queue identified by the CunrQueueID value (step 968). Theprocess thereafter returns to step 912 to wait for the next controlmessage.

FIG. 9C is a flow diagram of an embodiment of a process 970 performed bythe receiver HARQ entity to maintain the inactivity timers for the HARQchannels. The steps in this process may be performed for each TTI.

Initially, a determination is made whether or not an inactivity timerhas expired (step 972). Typically, only one inactivity timer, if any,expires in any given TTI since each timer is restarted at a differenttime whenever a control message is received for the HARQ channelassociated with the timer. If no inactivity timer has expired, then theprocess returns to step 972 and waits. Otherwise, the data in the softbuffer for the HARQ channel with the expired inactivity timer isdiscarded (step 974). The re-ordering entity handling the priority queuefor the last packet transmission on the HARQ channel with the expiredinactivity timer is then informed that this packet transaction iscompleted (step 976). The state of the HARQ channel with the expiredinactivity timer is then set to Inactive (step 978), and the processreturns to step 972.

FIG. 9D is a flow diagram of an embodiment of a process performed by thereceiver HARQ entity upon receiving a flushing indication on a controlmessage. This process may be performed for step 916 in FIG. 9A.Initially, the HARQ channels to be flushed are identified (step 982). Inone embodiment, these HARQ channels are identified as those used for aparticular priority queue identified by the Queue ID value included inthe control message itself. In other embodiments, the flushingindication may flush a specific HARQ channel, all HARQ channels, or someset of ascertainable HARQ channels. In any case, the data in the softbuffer for each identified HARQ channel is discarded (step 984). Thestate of each identified HARQ channel is then set to Inactive (step986). The re-ordering entity handling each identified HARQ channel isthen informed that the packet transaction on this channel is completed(step 988). The process then terminates.

Transmitter Re-Ordering Entity

The transmitter may maintain a window for each priority queue. Thiswindow would have the same size as that used by the receiver and is usedto flush out old data that will not be transmitted because the receiverwould discard the data anyway, as described above. At the transmitter,if packets for a given priority queue are transmitted in sequentialorder based on their TSNs, then the leading edge of the window may beset to the latest TSN of the packets sent. Thereafter, as each newpacket is transmitted, the window leading edge is moved to the TSN ofthis packet. As the window is slid forward for each new packettransmission, all packets with TSNs older than the trailing edge of thewindow are discarded.

At the transmitter, one “transmitter re-ordering entity” is responsiblefor determining packets to be transmitted on the HS-DSCH for eachpriority queue. The transmitter re-ordering entity is the protocol peerof the re-ordering entity at the transmitter. The transmitterre-ordering entity maintains the window for the associated priorityqueue. A local variable TxLeadWinEdge is used to indicate the leadingedge of the window and is initially set to “0”. The size of the windowis denoted by a local variable WindowSize.

FIG. 10 is a flow diagram of an embodiment of a process 1000 performedby the transmitter re-ordering entity for a particular priority queue.The steps shown in FIG. 10 are performed whenever a new packet isscheduled to be transmitted for this priority queue.

For the new packet to be sent, the transmitter re-ordering entity firstslides the window forward by incrementing the TxLeadWinEdge variable(step 1012). The TSN for the new packet is then set to the updatedTxLeadWinEdge value (step 1014). Any pending packets with TSNs outsidethe window are then discarded (step 1016). In particular, packets withTSN≦(TxLeadWinEdge−WindowSize) would fall outside the window and arediscarded. (Modulo-WindowSize operations are performed to account forwrap-around in the TSN number space.) The reason for discarding thesepackets is because they will fall outside the window at the receiver andwill be discarded if received. The new packet is then sent to the HARQentity designated to process the packet (step 1018). The process thenterminates.

If the channel conditions for the receiver are poor, then a flushingindication may be sent to the receiver when the transmission of all datain a data burst for a particular priority queue is completed. Thisflushing indication may be used to flush all HARQ channels used for thepriority queue, as described above. The flushing indication may be sent,for example, if the serving cell is not the one with the best uplink tothe UE and there is greater likelihood of not correctly receiving theNAK/ACK feedback from the UE.

Receiver Re-Ordering Entity

At the receiver, one receiver re-ordering entity is responsible forprocessing the data for each priority queue. The receiver re-orderingentity receives packets recovered by the HARQ entity for the associatedpriority queue, re-orders these packets, and delivers those packets thatare in sequence to higher layers. The re-ordering entity maintains awindow with a size that is replicated at the transmitter. A localvariable RxLeadWinEdge is used to indicate the latest TSN received forthe priority queue and is initially set to “0”. The size of the windowis denoted by a local variable WindowSize. Packets with TSNs within therange {(RxLeadwinEdge−WindowSize+1) . . . RxLeadWinEdge} are deemed tobe within the receiving window.

In one embodiment, each receiver re-ordering entity is able to startmultiple delay timers, one for each hole detected within the window. Thedelay timer is set long enough such that there is a high probability ofat least one control message transmission being sent for the HARQchannel used to send the missing packet before the timer expires. Eachdelay timer is associated with a particular Missing packet.

FIG. 6B is a diagram illustrating a window maintained by the receiverre-ordering entity. The packets are identified and referred to by theirTSNs. In an embodiment, from the receiver re-ordering entity'sperspective, each packet within the TSN number space is associated withone of four possible states: Delivered, Received, Missing, and Expected.A packet is considered (1) Delivered if it has been received from theHARQ entity and sent to higher layers, (2) Received if it has beenreceived from the HARQ entity but not yet delivered to higher layers,(3) Missing if it is part of a hole within the window, and (4) Expectedif it falls outside the window. A packet is deemed Missing if anotherpacket with a later TSN is received before it. A hole appears wheneverthere are one or more consecutive Missing packets in the window. Theremay be zero, one, or multiple holes in the window at any given moment.Initially, the state of all packets within the window is set toDelivered and those outside the window are set to Expected.

In an embodiment, for each packet in the Missing state (i.e., a Missingpacket), the receiver re-ordering entity maintains a MaskVector to markthe candidate HARQ channels for the Missing packet. The MaskVector isthus used to indicate whether or not each of the HARQ channels may beused to send the Missing packet. The MaskVector has a size equal to thenumber of all HARQ channels that may be used for transmission for allpriority queues, and includes one element for each possible HARQchannel.

The MaskVector for each Missing packet is “initialized” when the missingpacket is first detected. The initial candidate set would have theelement for each HARQ channel set to “1” except for the element for theHARQ channel for the received packet that was used to detect the missingpacket, which is set to “0”. A value of “1” indicates that theassociated HARQ channel may be used to send the Missing packet, and avalue of “0” indicates that the channel could not be used to send theMissing packet. Thus, the initial candidate set includes all HARQchannels except for the one known HARQ channel that could not be used tosend the missing packet. Thereafter, the element for each candidate HARQchannel may be set to “0” if it is determined that the channel could notbe used to send the Missing packet. This would be the case if: (1) a newpacket is sent on the HARQ channel, as determined by a change in the NewData indicator for the channel, (2) the inactivity timer for the channelexpires, or (3) a flushing indication is received for the channel.

The MaskVector for each Missing packet is also “modified” when the delaytimer applicable for the Missing packet expires. The modified candidateset would be purged of all HARQ channels that are not active when thedelay timer expires (by setting the elements in the MaskVector for theseHARQ channels to “0”). The process to eliminate the remaining HARQchannels from the candidate set would then proceed as before.

FIGS. 11A and 11B show a flow diagram of an embodiment of a process 1100performed by the receiver re-ordering entity for a particular priorityqueue. Initially, the receiver re-ordering entity receives a packet withTSNr on HARQ channel Hx from the HARQ entity (step 1112). Adetermination is then made whether or not the just-received packet(i.e., the current packet) is a new packet (step 1114). The currentpacket is deemed a new packet if TSNr falls outside the window, and isdeemed a retransmission of a pending packet if TSNr falls within thewindow. If the current packet is a new packet, then the process proceedsto step 1140.

Otherwise, if TSNr falls within the window, then the current packet iseither (1) a duplicate of a prior received packet or (2) one for aMissing packet that will partially or completely fill a hole within thewindow. A determination is then made whether or not the current packetis one that has already been received or delivered (step 1116). If theanswer is yes, then the current packet is a duplicate and discarded(step 1118), and the process terminates.

Otherwise, if the answer is no in step 1116, then the current packet isfor a Missing packet within the window. In that case, the MaskVector ofeach earlier Missing packet (i.e., those with TSN earlier than TSNr) isupdated by setting the element corresponding to HARQ channel Hx to “0”(step 1120). This is because a later packet with TSNr was received onthis channel and could not be the one used to send the earlier Missingpacket. Each time the MaskVector is updated, it is also checked todetermine whether or not all elements of the MaskVector are “0s”, whichwould indicate that the candidate set is empty and that the Missingpacket is lost. If the MaskVector includes all “0s”, then all Receivedpackets that are stalled by this Missing packet are delivered to higherlayers, and all packets earlier than this packet are set to Delivered.

The state of the current packet is then set to Received (step 1122). AllReceived packets (if any) not currently stalled by a hole are deliveredto higher layers (1124). In particular, consecutive Received packetsstarting from the left side of the window and continuing until the firsthole (or a Missing packet) is detected are identified and sent to higherlayers. The state of these delivered packets is also set to Delivered.

In an embodiment, one delay timer is maintained for the last packet ineach “original” hole, which is a hole that occurs whenever a new packetis received by the re-ordering entity and there are one or more Expectedpackets earlier than (or to the left of) the new packet. The state ofthe Expected packets in the hole is changed to Missing. This isdescribed in further detail below. Subsequently, a packet may bereceived by the re-ordering entity for a Missing packet in this hole. Ifthe hole is a width of one packet, then the received packet wouldcompletely cover the hole and the delay timer is canceled. Otherwise, ifthe hole covers multiple packets and the current packet is the lastMissing packet in this hole, then the delay timer is moved to the (new)last Missing packet in the partially covered hole. And if the holecovers multiple packets and the current packet is not the last Missingpacket in the hole, then the delay timer is not affected. With thisimplementation, only one delay timer needs to be maintained for allmissing packets within an original hole (since they were detected at thesame time), even if this hole is subsequently chopped up into multipleholes by packets received later by the re-ordering entity.

Thus, a determination is made whether or not a delay timer has beenstarted for the current packet (step 1126). If the answer is no, thenthe process terminates. Otherwise, a determination is made whether ornot there is a hole to the left of the current packet (step 1128). Ifthe answer is no, then the delay timer for the current packet iscanceled, since this would indicate that the current packet completelyfills the hole, in which case the delay timer does not need to bemaintained (step 1130). Otherwise, if the current packet does not fill ahole, then no action is performed with respect to the delay timer. Ineither case, the process then terminates.

Back in step 1114, if the current packet is a new packet, then the stateof this packet is set to Received (step 1140). The MaskVector for eachMissing packet in the window is then updated and checked, and packetsmay be flushed by the re-ordering entity to higher layers as a result,as described above for step 1120 (step 1142). The window is then movedforward by setting the leading edge of the window, or RxLeadWinEdge, toTSNr (step 1144). All Received packets outside the window are thendelivered to higher layers (step 1146), the state of all packets outsidethe window is set to Expected (step 1148), and all delay timers thathave been set for packets outside the window are stopped (step 1150).Received packets (if any) not currently stalled by a hole are deliveredto higher layers (1152). This may be performed as described above forstep 1124.

A determination is then made whether or not a hole exists just to theleft of the current packet (step 1154). This determination can be madeby checking whether the state of the packet with TSNr−1 is Expected. Ifthe answer is no, then the process terminates. Otherwise, if there is ahole, then a delay timer is started for the last packet in the hole(i.e., with TSNr−1) (step 1156). Each Expected packet in this hole isthen set to Missing, and the MaskVector for each such packet isinitialized by setting the element corresponding to HARQ channel Hx to“0” and all other elements to “1” (step 1158). The process thenterminates.

For the embodiment described above, one delay timer is used for allMissing packets in each original hole (i.e., a hole detected with a newpacket that moves the window forward). This timer is associated with thelast Missing packet in the hole but is applicable to (or referenced by)all of the Missing packets in the hole. In one implementation, atimer_over flag is used for each Missing packet to indicate whether ornot its applicable delay timer (i.e., the first delay timer to the rightof the packet) has expired. When the original hole is detected, thetimer_over flag for each Missing packet in the hole may be reset to “0”to indicate that the applicable delay timer has not expired (step 1158).And when the delay timer expires, the timer_over flags for all Missingpackets covered by this timer are set to “1”, and MaskVectors of allthese Missing packets are also modified, as described above, to removedHARQ channels that are not active at this time or used for anotherpriority queue. This implementation is described in further detailbelow.

The MaskVectors for the Missing packets are updated/revised based onvarious events such as (1) whenever the HARQ entity indicates that apacket transaction on a given HARQ channel is completed, and (2) wheneach delay timer maintained for an associated Missing packet expires.

FIG. 11C shows a flow diagram of an embodiment of a process 1160performed by the receiver re-ordering entity whenever an indication isreceived that a delay timer has expired. Initially, a determination ismade whether or not a delay timer has expired (step 1162). If the answeris no, then the process terminates. Otherwise, if a delay timer hasexpired, then the TSN of the Missing packet associated with the expireddelay timer is determined and denoted as TSNe (step 1164). MultipleMissing packets may rely on this delay timer since only one ismaintained for all missing packets in each original hole, as describedabove. The timer_over flag for each Missing packet covered by thisexpired delay timer is then set to “1” to indicate the timer for packethas expired (step 1166). The Missing packets covered by this expireddelay timer include those with TSN earlier than TSNe. The MaskVector foreach Missing packet covered by this delay timer is then “modified”(i.e., to revise the candidate set for the Missing packet) (step 1168).To modify the MaskVector for a Missing packet, each HARQ channel isconsidered, and if the channel is not Active or if the channel is usedfor another priority queue, then the corresponding element in theMaskVector is set to “0”. The HARQ channels corresponding to theelements in the MaskVector that are still set to “1” are the remainingcandidate HARQ channels at this time. If a MaskVector is revised, thenit is checked to determine whether or not packets should be flushed tohigher layers. The process then terminates.

FIG. 11D shows a flow diagram of an embodiment of a process 1170performed by the receiver re-ordering entity for a completed transactionon a particular HARQ channel. Initially, determination is then madewhether an indication has been received from the receiver HARQ entitythat a packet transaction has been completed on an HARQ channel (step1172). If the answer is yes, then for each Missing packet for which theapplicable delay timer has expired (i.e., with the timer_over flag resetto “0”), the element in the MaskVector corresponding to the HARQ channelis set to “0” (step 1174). Again, if a MaskVector is updated, then it ischecked to determine whether or not packets should be flushed to higherlayers. The processing to be performed for a completed transaction on aHARQ channel is described in further detail in the pseudo-code below.The process then terminates.

In the embodiment described above, each receiver re-ordering entity isable to start multiple delay timers, one for each original hole detectedwithin the window. In another embodiment, each re-ordering entity canhave one delay timer running at any given moment. Whenever an originalhole is detected, the delay timer for the re-ordering entity can bestarted if it is not currently running. If another original hole issubsequently detected while the delay timer is running, then no delaytimer is started at that moment for the Missing packets in the secondoriginal hole. If the delay timer thereafter expires, then the Missingpackets covered by this delay timer (i.e., the Missing packets with TSNsearlier than the TSNe of the Missing packet associated with the delaytimer) are updated as shown in steps 1162 through 1166 in FIG. 11C. Inaddition (after step 1166), a determination is made whether or not thereare any Missing packets with TSNs later than TSNe. If the answer is yes,then the delay timer is started again and associated with the latestMissing packet.

This alternative embodiment reduces the number of delay timers needed tobe maintained by each re-ordering entity to one. However, thisembodiment may double the delay timer value for a Missing packet in theworse case. For example, the delay timer may be started for a firstMissing packet, and a second Missing packet may be detected in the nexttransmission interval. The delay timer for the second Missing packetcannot be started until the delay timer for the first Missing packetexpires. The second Missing packet would then need to wait for theexpiration of the delay timer for both the first Missing packet plus thesecond Missing packet. This alternative embodiment is described infurther detail in the pseudo-codes shown below.

FIG. 12 shows a flow diagram of an overall process 1200 performed by are-ordering entity to receive packets from the HARQ entity and deliverpackets to higher layers. Initially, packets that have been decodedcorrectly are received from the HARQ entity (step 1212). Missing packetsamong the received packets are then detected (step 1214). This may beachieved based on the TSNs of the received packets as described above.If missing packets are detected, then delivery of received packets laterthan the detected missing packets to higher layers is stalled (step1216). A determination is then made for each missing packet whether itis either (1) subsequently received from the HARQ entity or (2) lost, bysuccessively eliminating HARQ channels that may be used to send themissing packet, as also described above (step 1218). Received packetsthat have been stalled by each missing packet are thereafter deliveredto higher layers after the missing packet is determined to be lost orreceived from the HARQ entity (step 1220).

Pseudo-codes for a specific implementation of the processes describedabove in FIGS. 8 through 1 IC are shown below.

Transmitter HARQ Entity

When scheduled for a (re)transmission for a particular priority queue,the transmitter:

-   1—if this is the first transmission for the packet:    -   2—toggle the New Data indicator;-   1—set the QueueID field to the priority queue of the packet being    transmitted;-   1—end the procedure.    When receiving an ACK:-   1—discard the current packet being transmitted;-   1—indicate to the scheduler that this HARQ entity is available;-   1—end the procedure.

Receiver HARQ Entity

Upon reception of a control channel transmission sent for the receiver:

-   1—if the control message contains a flushing indication:    -   2—handle the flushing indication for the priority queue        indicated in the QueueID field (see below);    -   2—end the procedure.-   1—start/restart the inactivity timer (TM1) for the HARQ channel    identified by the control message;-   1—if the identified HARQ channel is in Inactive state:    -   2—if CurrNewData has the same value as the New Data indicator:        -   3—discard the received packet;        -   3—send an ACK on the uplink;        -   3—end the procedure.    -   2—else:        -   3—set the HARQ channel to Active state;        -   3—set CurrNewData to the value of the New Data indicator;        -   3—set CurrQueueID to the value of the Queue ID field;        -   3—store the received packet transmission in a soft buffer;-   1—else (if the HARQ channel is in Active state):    -   2—if CurrNewData=New Data indicator:        -   3—soft combine the received packet with the accumulated            prior transmissions in the soft buffer;    -   2—else:        -   3—discard the data currently in the soft buffer;        -   3—indicate to the re-ordering entity corresponding to            CurrQueueID that the packet transaction is completed (see            below);        -   3—set CurrNewData to the value of the New Data indicator;        -   3—set CurrQueueID to the value of the Queue ID field;        -   3—store the received packet transmission in the soft buffer;-   1—attempt to decode the packet in the soft buffer;-   1—if the decoding is successful:    -   2—send an ACK on the uplink;    -   2—set the HARQ channel to Inactive state;    -   2—deliver the recovered packet to the re-ordering entity        corresponding to CurrQueueID (see below);-   1—else:    -   2—send a NAK on the uplink;-   1—end the procedure.    Upon expiration of inactivity timer (TM1) for a given HARQ channel:-   1—discard the data currently in the soft buffer;-   1—indicate to the re-ordering entity corresponding to CurrQueueID    that the packet transaction is over (see below);-   1—set the HARQ channel to Inactive state;-   1—end the procedure.    Upon reception of a flushing indication for a given priority queue:-   1—for each HARQ channel with CurrQueueID equal to the Queue ID value    in the control message for the flushing indication:    -   2—do not attempt to receive data;    -   2—discard the data in the soft buffer;    -   2—set the HARQ channel to Inactive state;    -   2—indicate to the re-ordering entity corresponding to        CurrQueueID that the packet transaction is over;-   1—end the procedure.

Transmitter Re-Ordering Entity

When the associated priority queue is scheduled for transmission, thetransmitter re-ordering entity:

-   1—increment TxLeadWinEdge;-   1—set the TSN for the new packet to TxLeadWinEdge;-   1—discard any pending packets with TSN≦TxLeadWinEdge−WindowSize;-   1—submit the new packet to the HARQ entity designated by the    scheduler;-   1—end the procedure.

Receiver Re-ordering Entity

For the embodiment wherein one delay timer is maintained for eachoriginal hole.

When a new packet with TSNr is delivered by the HARQ entity, thereceiver re-ordering entity:

-   1—if the received packet is within the receiving window    (RxLeadWinEdge−WindowSize≦TSNr≦RxLeadWinEdge):    -   2—for each TSNi in state Missing:        -   3—if TSNi<TSNr:            -   4—set the element in MaskVector corresponding to this                HARQ channel to “0”;            -   4—if all the elements in MaskVector are equal to 0:                -   5—perform flushing procedure (see below) for TSNi    -   2—if the state of TSNr is Received or Delivered:        -   3—discard the received packet;    -   2—else (the state for TNSr is Missing):        -   3—if the state of all packets within the receiving window            with TSN<TSNr is Delivered then:            -   4—if a delay timer (TM2) associated with TSNr is started                then stop the timer;            -   4—deliver the packet to higher layers;            -   4—set the state of TSNr to Delivered;            -   4—for each TSNJ inside the receiving window, starting                with TSNr+1:                -   5—if the state of TSNj is Expected or Missing:                -    6—stop iterating over TSNj.                -   5—else, if the state of TSNj is Received:                -    6—deliver the data for TSNj to higher layer;                -    6—set the state of TSNj to Delivered;                -    6—if a delay timer is associated with TSNj, then                    stop the timer;                -    6—go to next TSNj;        -   3—else:            -   4—set the state of TSNr to Received;-   1—else (received packet is outside the receiving window):    -   2—for each TSNi in state Missing:        -   3—set the element in MaskVector corresponding to this HARQ            channel to “0”;        -   3—if all the elements in MaskVector are equal to “0”:            -   4—perform flushing procedure for TSNi    -   2—set RxLeadWinEdge to TSNr;    -   2—deliver to higher layers all the data associated with TSNs        outside the receiver window with state Received;    -   2—stop all delay timer TM2 associated with TSNs outside the        receiver window;    -   2—set the state for all TSNs outside the receiver window to        Expected;    -   2—if the state of all packets within the receiving window with        TSN<TSNr is Received or Delivered then:        -   3—deliver the packets to higher layers;        -   3—set the state of TSNr to Delivered;    -   2—else:        -   3—set the state of TSNr to Received;        -   3—start a delay timer TM2 associated with TSNr−1;        -   3—for each TSNj inside the receiving window with TSNj<TSNr            with state Expected:            -   4—set the state of TSNj to Missing;            -   4—reset the timer_over flag to “0”;            -   4—in the MaskVector associated with TSNj:                -   5—set the element corresponding to this HARQ channel                    to “0”;                -   5—set the elements corresponding to other HARQ                    channels to “1”;-   1—end the procedure;    When the HARQ entity indicates that a packet transaction is over for    a particular HARQ channel:-   1—for each TSNi in state Missing for which the timer_over flag is    set to 1: 2—set the element in MaskVector corresponding to this HARQ    channel to “0”;    -   2—if all the elements in MaskVector are equal to “0”:        -   3—perform flushing procedure for TSNi-   1—end the procedure    When a delay timer (TM2) expires:-   1—consider each TSN in state Missing, with TSN<=to the TSN    associated with the timer:    -   2—set the timer_over flag to “1”;    -   2—consider the MaskVector variable for this TSN;    -   2—for each HARQ entity:        -   3—if the HARQ entity is not in Active state or CurrQueueID            is different from the priority queue of this re-ordering            entity:            -   4—set the element of the MaskVector corresponding to                this HARQ channel to “0”;-   1—end the procedure;    Flushing Procedure—when all the elements in MaskVector for TSNi are    equal to “0”:-   1—for each TSNj within the receiving window and earlier than or    equal to TSNi:    -   2—if the state of TSNj is Received then deliver the associated        data to higher layer;    -   2—set the state of TSNj to Delivered;-   1—for each TSNJ inside the receiving window, starting with TSNi+1:    -   2—if the state of TSNj is Expected or Missing:        -   3—stop iterating over TSNj.    -   2—else, if the state of TSNJ is Received:        -   3—deliver the associated data to higher layer;        -   3—set the state of TSNj to Delivered;        -   3—go to next TSNJ;-   1—return;    For the embodiment wherein one delay timer is maintained for each    re-ordering entity.    When a new packet with TSNr is delivered by the HARQ entity, the    receiver re-ordering entity:-   1—if the received packet is within the receiving window    (RxLeadWinEdge—WindowSize≦TSNr<RxLeadWinEdge):    -   2—for each TSNi in state Missing:        -   3—if TSNi<TSNr:            -   4—set the element in MaskVector corresponding to this                HARQ channel to “0”;            -   4—if all the elements in MaskVector are equal to 0:                -   5—perform flushing procedure (see below) for TSNi    -   2—if the state of TSNr is Received or Delivered:        -   3—discard the received packet;    -   2—else (the state for TNSr is Missing):        -   3—if the state of all packets within the receiving window            with TSN<TSNr is Delivered then:            -   4—if a delay timer (TM2) associated with TSNr is started                then stop the timer;            -   4—deliver the packet to higher layers;            -   4—set the state of TSNr to Delivered;            -   4—for each TSNj inside the receiving window, starting                with TSNr+1:                -   5—if the state of TSNj is Expected or Missing:                -    6—stop iterating over TSNj.                -   5—else, if the state of TSNj is Received:                -    6—deliver the data for TSNj to higher layer;                -    6—set the state of TSNj to Delivered;                -    6—if a delay timer is associated with TSNj, then                    stop the timer;                -    6—go to next TSNj;        -   3—else:            -   4—set the state of TSNr to Received;-   1—else (received packet is outside the receiving window):    -   2—for each TSNi in state Missing:        -   3—set the element in MaskVector corresponding to this HARQ            channel to “0”;        -   3—if all the elements in MaskVector are equal to “0”:            -   4—perform flushing procedure for TSNi    -   2—set RxLeadWinEdge to TSNr;    -   2—deliver to higher layers all the data associated with TSNs        outside the receiver window with state Received;    -   2—stop all delay timer TM2 associated with TSNs outside the        receiver window;    -   2—set the state for all TSNs outside the receiver window to        Expected;    -   2—if the state of all packets within the receiving window with        TSN<TSNr is Received or Delivered then:        -   3—deliver the packets to higher layers;        -   3—set the state of TSNr to Delivered;    -   2—else:        -   3—set the state of TSNr to Received;        -   3—if the delay timer TM2 for this re-ordering entity is not            running, then:            -   4—start a delay timer TM2 associated with TSNr−1;        -   3—for each TSNj inside the receiving window with TSNj<TSNr            with state Expected:            -   4—set the state of TSNj to Missing;            -   4—reset the timer_over flag to “0”;            -   4—in the MaskVector associated with TSNj:                -   5—set the element corresponding to this HARQ channel                    to “0”;                -   5—set the elements corresponding to other HARQ                    channels to “1”;-   1—end the procedure;    When the HARQ entity indicates that a packet transaction is over for    a particular HARQ channel:-   1—for each TSNi in state Missing for which the timer_over flag is    set to 1: 2—set the element in MaskVector corresponding to this HARQ    channel to “0”;    -   2—if all the elements in MaskVector are equal to “0”:        -   3—perform flushing procedure for TSNi-   1—end the procedure    When a delay timer (TM2) expires:-   1—consider each TSN in state Missing, with TSN<=to the TSN    associated with the timer:    -   2—set the timer_over flag to “1”;    -   2—consider the MaskVector variable for this TSN;    -   2—for each HARQ entity:        -   3—if the HARQ entity is not in Active state or CurrQueueID            is different from the priority queue of this re-ordering            entity:            -   4—set the element of the MaskVector corresponding to                this HARQ channel to “0”;-   1—if there is any TSN in state Missing:    -   2—start the delay timer and associated it with the TSN of the        latest packet in state Missing;-   1—end the procedure;    Flushing Procedure—when all the elements in MaskVector for TSNi are    equal to “0”:-   1—for each TSNj within the receiving window and earlier than or    equal to TSNi:    -   2—if the state of TSNj is Received then deliver the associated        data to higher layer;    -   2—set the state of TSNj to Delivered;-   1—for each TSNJ inside the receiving window, starting with TSNi+1:    -   2—if the state of TSNj is Expected or Missing:        -   3—stop iterating over TSNj.    -   2—else, if the state of TSNJ is Received:        -   3—deliver the associated data to higher layer;        -   3—set the state of TSNj to Delivered;        -   3—go to next TSNj;-   1—return;

The pseudo-code for a specific implementation is shown above to providea clearer understanding of the processing performed by various entitiesat the transmitter and receiver. Other implementations may also becontemplated, as would be recognized by one skilled in the art based onthe teachings described herein, and these various other implementationsare also within the scope of the invention.

The techniques described herein may be used to provide improved stallavoidance performance for systems having an underlying retransmissionmechanism (e.g., HARQ) and higher layers that require data in sequentialorder. These techniques may be used for various communication systemssuch as, for example, W-CDMA systems, cdma2000 systems, and so on. Thesetechniques may also be used for other types of communication systems(e.g., TDMA and FDMA systems).

FIG. 13 is a block diagram of an embodiment of Node B 104 and UE 106. Onthe downlink, data for the HS-DSCH and HS-SCCH for a particular UEdesignated to receive HSDPA transmission is received and processed(e.g., formatted, encoded, and so on) by a transmit (TX) data processor1312. The processing for the HS-DSCH and HS-SCCH may be performed asdescribed in the applicable standard documents for W-CDMA Release 5,including TS.25-321 V5.0.0, TS.25-308 V5.2.0, and 25-212 V5.0.0, whichare all incorporated herein by reference. These and other documents forW-CDMA Release 5 are publicly available.

The processed data is then provided to a modulator (MOD) 1314 andfurther processed (e.g., channelized, spread, and so on) to providemodulated data. A transmitter (TMTR) unit 1316 then converts themodulated data into one or more analog signals, which are furtherconditioned (e.g., amplified, filtered, and frequency upconverted) toprovide a downlink signal. The downlink signal is routed through aduplexer (D) 1322 and transmitted via an antenna 1324 to the designatedUE.

At the UE, the downlink signal is received by an antenna 1352, routedthrough a duplexer 1354, and provided to a receiver (RCVR) unit 1356.Receiver unit 1356 conditions (e.g., filters, amplifies, and frequencydownconverts) the received signal and further digitizes the conditionedsignal to provide samples. A demodulator 1358 then receives andprocesses (e.g., despreads, channelizes, and data demodulates) thesamples to provide symbols. Demodulator 1358 may implement a rakereceiver that can process multiple instances (or multipath components)of the received signal to provide combined symbols. A receive (RX) dataprocessor 1360 then decodes the symbols, checks the received packets,and provides the decoded data. The processing by demodulator 1358 and RXdata processor 1360 is complementary to the processing by modulator 1314and TX data processor 1312, respectively.

In one embodiment, RX data processor 1360 performs the processing forthe physical layer and part of the MAC layer (e.g., the HARQ entity),and a controller 1370 performs some of the processing for the MAC layer(e.g., the re-ordering entity) and further implements part of HARQ. Forthis embodiment, RX data processor 1360 may provide (1) the decoded datafor each packet decoded correctly, (2) the status of each packettransmission (e.g., ACK or NAK), (3) indications of expired inactivityand delay timers, and so on. Controller 1370 may then detect for missingpackets and provide packets to higher layers as they are received andavailable. Controller 1370 further provides to a TX data processor 1382the appropriate ACK/NAK feedback for the HARQ operation.

On the uplink, data for the uplink and ACK/NAK feedback information areprocessed (e.g., formatted, encoded, and so on) by TX data processor1382, further processed (e.g., channelized, spread, and so on) bymodulator 1384, and conditioned (e.g., converted to analog signals,amplified, filtered, and frequency upconverted) by a transmitter unit1386 to provide an uplink signal. The uplink signal is then routedthrough duplexer 1354 and transmitted via antenna 1352 to the basestation.

At the Node B, the uplink signal is received by antenna 1324, routedthrough duplexer 1322, and provided to a receiver unit 1342. Receiverunit 1342 conditions (e.g., frequency downconverts, filters, andamplifies) the received signal and further digitizes the conditionedsignal to provide a stream of samples. A demodulator 1344 then processes(e.g., despreads, channelizes, and so on) the samples to providesymbols, and an RX data processor 1346 further processes the symbols toprovide the decoded data for the UE. The data processing for thedownlink and uplink is described by the W-CDMA standard documents.

A controller 1330 receives the ACK/NAK feedback from RX data processor1346 and directs the retransmission of packets for HARQ, as necessary.Controllers 1330 and 1370 further control the processing at the Node Band the UE, respectively. Each controller may also be designed toimplement all or a portion of the techniques described herein for HARQtransmission/retransmission. Program codes and data required bycontrollers 1330 and 1370 may be stored in memory units 1332 and 1372,respectively.

The techniques described herein for improving stall avoidanceperformance may be implemented by various means. For example, thesetechniques may be implemented in hardware, software, or a combinationthereof. For a hardware implementation, the elements used to implementthe techniques (e.g., the elements that perform the processes shown inFIGS. 8 through and 11A) may be implemented within one or moreapplication specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, micro-controllers, microprocessors,other electronic units designed to perform the functions describedherein, or a combination thereof.

For a software implementation, these techniques may be implemented withmodules (e.g., procedures, functions, and so on) that perform thefunctions described herein. The software codes may be stored in a memoryunit (e.g., memory units 1332 and 1372 in FIG. 13) and executed by aprocessor (e.g., controllers 1330 and 1370). The memory unit may beimplemented within the processor or external to the processor, in whichcase it can be communicatively coupled to the processor via variousmeans as is known in the art.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. A method for wireless communications, comprising: receiving one ormore packets from a group of packets transmitted in a hybrid automaticretransmission instance; detecting at least one missing packet;determining a candidate set of hybrid automatic retransmission channelsthat may be used to transmit the detected missing packet; anddetermining whether the missing packet is either subsequently receivedor lost by successively eliminating at least one hybrid automaticretransmission channels from said candidate set if a condition is met.2. The method as recited in claim 1, further comprising: deliveringreceived packets, after the missing packet is determined to be lost orreceived, to a higher communication layer.
 3. The method of claim 1,wherein said packets in said group are transmitted in sequential orderbased on transmission sequence numbers (TSNs) assigned to said packets.4. The method of claim 3, wherein said at least one missing packet isdetected based on the TSNs of said received one or more packets.
 5. Themethod of claim 1, further comprising stalling delivery of packets to ahigher communication layer in response to the missing packet beingdetected.
 6. The method of claim 1, wherein said condition comprises anyof: determining inactivity of the channel for a period of time,recovering the missing packet on the channel, detecting a new packet onthe channel, receiving an indication to flush the channel, and receivinga priority of the missing packet.
 7. The method of claim 1, wherein saiddetermining said candidate set of said hybrid automatic retransmissionchannels comprises identifying all active channels.
 8. The method ofclaim 1, wherein a channel on which a subsequent packet used to detectthe missing packet is received is not included in said candidate set. 9.The method of claim 1, wherein the missing packet is determined to belost in response to all said identified channels being eliminated. 10.The method of claim 1, wherein said determining said candidate set ofsaid hybrid automatic retransmission channels comprises using a delaytimer.
 11. The method of claim 1, wherein said determining saidcandidate set of said hybrid automatic retransmission channels comprisesidentifying only channels used for a specified priority queue.
 12. Themethod of claim 1, wherein said eliminating each channel upon saidcondition being met comprises flushing the channel in response to aflushing indication.
 13. An apparatus, comprising: means for receivingone or more packets from a group of packets transmitted in a hybridautomatic retransmission instance; means for detecting at least onemissing packet; means for determining a candidate set of hybridautomatic retransmission channels that may be used to transmit thedetected missing packet; and means for determining whether the missingpacket is either subsequently received or lost by successivelyeliminating at least one hybrid automatic retransmission channels fromsaid candidate set if a condition is met.
 14. The apparatus as recitedin claim 13, further comprising: means for delivering received packets,after the missing packet is determined to be lost or received, to ahigher communication layer.
 15. An access terminal, comprising: adisplay screen; one or more input keys; and a controller configured toreceive one or more packets from a group of packets transmitted in ahybrid automatic retransmission instance, to detect at least one missingpacket, to determine a candidate set of hybrid automatic retransmissionchannels that may be used to transmit the detected missing packet, andto determine whether the missing packet is either subsequently receivedor lost by successively eliminating at least one hybrid automaticretransmission channels from said candidate set if a condition is met.16. An access point, comprising: an antenna; and a controller configuredto receive one or more packets from a group of packets transmitted in ahybrid automatic retransmission instance, to detect at least one missingpacket, to determine a candidate set of hybrid automatic retransmissionchannels that may be used to transmit the detected missing packet, andto determine whether the missing packet is either subsequently receivedor lost by successively eliminating at least one hybrid automaticretransmission channels from said candidate set if a condition is met.17. A machine-readable medium comprising instructions executable by amachine for receiving data, the instructions configured when executed tocause the machine to: receive one or more packets from a group ofpackets transmitted in a hybrid automatic retransmission instance;detect at least one missing packet; determine a candidate set of hybridautomatic retransmission channels that may be used to transmit thedetected missing packet; and determine whether the missing packet iseither subsequently received or lost by successively eliminating atleast one hybrid automatic retransmission channel from said candidateset if a condition is met.